It is anecdotally recognized that prolonged recovery time is necessary after marathon running. However, several recent studies indicate that physiological recovery occurs within a few days after marathon running. We report changes in examined physiological characteristics one week before and one week after marathon running and subsequent 20-km performance at two weeks after the race in a well-trained runner. A male runner (age: 34 years, height: 180 cm, weight: 78 kg) completed a marathon race in 2 h 53 min 35 s running at a speed of 14.6 km/h. Maximal oxygen uptake, ventilatory threshold, and running economy one week before (PRE) and one week after (POST) marathon running was assessed. Perceived muscle soreness was evaluated before and up to 7 days after the race. The training data was analyzed from six weeks before to two weeks after the marathon race, as recorded in his training diary. There were small differences in the examined physiological characteristics between PRE and POST (-2.1% to 4.5%). Perceived muscle soreness peaked at 1 day after the race, but it returned to pre-race value 7 days after marathon running. Thirteen days after completing the marathon, he finished a 20-km race in 1 h 15 min 32 s running at a speed of 15.9 km/h. No changes in the examined physiological characteristics were observed one week before and one week after marathon running in a well-trained runner. Thus, we conclude that a well-trained runner can recover relatively soon after marathon running.